使用多个选择作为列优化查询

Question

I have a query I made:

 SELECT DISTINCT player_1 AS player, 
                (SELECT COUNT(*) FROM results WHERE player_1=player OR player_2=player) AS since_start_matches, 
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals=0) AS since_start_ht_0,
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals=1) AS since_start_ht_1,
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals=2) AS since_start_ht_2,
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals=3) AS since_start_ht_3,
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals=4) AS since_start_ht_4,
                (SELECT COUNT(*) FROM results WHERE (player_1=player OR player_2=player) AND ht_total_goals>=5) AS since_start_ht_5_plus
FROM results ORDER BY player

The results table has 25000 entries and it takes around 7 seconds to do this query, which is far too long. The query is incredibly inefficient as each column I'm creating is searching again on the same table but with different conditions.

I tried indexing the columns of interest in my where clause. This knocks off a couple of seconds. But it's still too slow.

What is the best approach to handle this kind of query?

I'm using MariaDB 10.2

Answer 1

Unpivot the data then aggregation:

 SELECT player, 
        COUNT(*) AS since_start_matches, 
        SUM(ht_total_goals=0) AS since_start_ht_0,
        SUM(ht_total_goals=1) AS since_start_ht_1,
        SUM(ht_total_goals=2) AS since_start_ht_2,
        SUM(ht_total_goals=3) AS since_start_ht_3,
        SUM(ht_total_goals=4) AS since_start_ht_4,
        SUM( ht_total_goals>=5) AS since_start_ht_5_plus
FROM ((SELECT player_1 as player, ht_total_goals
       FROM results
      ) UNION ALL
      (SELECT player_2 as player, ht_total_goals
       FROM results
      )
     ) p
GROUP BY player

Answer 2

You can use the LEFT JOIN and conditional aggregation as follows:

SELECT  player_1 AS player, 
                COUNT(T2.player_1) AS since_start_matches, 
                SUM(CASE WHEN T2.ht_total_goals=0 THEN 1 END) AS since_start_ht_0,
                SUM(CASE WHEN T2.ht_total_goals=1 THEN 1 END) AS since_start_ht_1,
                SUM(CASE WHEN T2.ht_total_goals=2 THEN 1 END) AS since_start_ht_2,
                SUM(CASE WHEN T2.ht_total_goals=3 THEN 1 END) AS since_start_ht_3,
                SUM(CASE WHEN T2.ht_total_goals=4 THEN 1 END) AS since_start_ht_4,
                SUM(CASE WHEN T2.ht_total_goals>=5 THEN 1 END) AS since_start_ht_5_PLUS
FROM results T1 LEFT JOIN results T2 
ON (T2.player_1=T.player OR T2.player_2=T.player)
GROUP BY T1.PLA

YER_1 ORDER BY player